Japanese Patent Application Publication No. 2006-324525 discloses a signal transmitting apparatus which transmits a signal using electromagnetic induction of a coil. This signal transmitting apparatus has a transformer (sending coil, receiving coil) and a detecting circuit. If the sending coil is driven by the inputted signal, a received signal is outputted from the receiving coil by the electromagnetic induction. The detecting circuit detects the inputted signal from the received signal outputted from the receiving coil. Thereby the signal is transmitted from a sending coil side to a receiving coil side.